PROJECT SUMMARY Child and adolescent obesity continue to be serious public health challenges of the 21st century. Recently, the role of the built- and policy (B&P) environments in contributing to diet, activity and BMI has received significant attention. But, evaluating these relationships is challenging due to concerns about selection and heterogeneity. Individuals select neighborhoods based on preferences towards health and other factors, which may bias estimates. Because random assignment is infeasible, experts have called for natural- and quasi- experimental methods that leverage exogenous variation. Moreover, environments may not affect all individuals equally and can average out to small or null effects, yielding misleading conclusions. Such heterogeneity has thus far only been examined by demographic characteristics. However, evidence on environments? effects is mixed even within these subgroups, suggesting that other factors may be at work. An emerging literature suggests that time-and risk (T&R) preferences (e.g. future-orientation and risk-aversion) may play such a role. T&R preferences vary considerably and have been linked with health behaviors. Therefore, it is possible that individuals who vary in their future-orientation and risk-aversion are differentially impacted by the B&P environment. However, to our knowledge, this has not been examined empirically. Adolescents represent a key subpopulation in which to study these issues; their obesity rates have quadrupled during the past thirty years, and their T&R preferences, health behaviors, and interactions with the B&P environment are evolving towards independence, making this a critical time for interventions. Our goal is to exploit a rare opportunity to estimate the effects of B&P environments on obesogenic behaviors and outcomes among adolescents while addressing selection and heterogeneity. We propose to expand our NIH-funded Military Teenagers? Environment, Exercise, and Nutrition Study (M- TEENS), which leveraged a natural experiment due to the compulsory (re)location of Army families. M-TEENS collected up to 3 waves of data on diet, activity and BMI from 1519 12-13 year old children in Army families. Our proposed extension will collect 2 additional waves of data (2017 & 2018), yielding a 5-year longitudinal panel with rarely-available exogenous within-child changes in the B&P environment. A novel contribution of the proposed study is the examination of whether the environment?s effects vary by adolescents? and their parents? T&R preferences. This is a time-sensitive application; our cohort will complete high-school at the end of the proposed data collection, making their relocations and, therefore environments, less exogenous thereafter. This study is likely to have a high impact because it addresses a highly significant health issue, combines a natural experiment study design with longitudinal data, and is highly innovative in its focus on the role of adolescents? and parents? preferences in understanding environments? effects.